In ITU-R (International Telecommunication Union Radio communication sector), a standardization task for IMT (International Mobile Telecommunication)-Advanced (i.e., the next-generation mobile communication system after the third generation) is being in progress. IMT-Advanced sets its goal to support IP (Internet Protocol)-based multimedia service at the data transfer rate of 1 Gbps in stop and slow-speed moving states and at the data transfer rate of 100 Mbps in a fast-speed moving state.
3GPP (3rd Generation Partnership Project) is a system standard to satisfy the requirements of IMT-Advanced and is preparing for LTE-A (Long Term Evolution-Advanced). LTE (Long Term Evolution) according the 3GPP (3rd Generation Partnership Project) standardization system is part of E-UMTS (Evolved-UMTS) which uses an E-UTRAN (Evolved-Universal Terrestrial Radio Access Network). The LTE adopts OFDMA (Orthogonal Frequency Division Multiple Access) in downlink and adopts SC-FDMA (Single Carrier-Frequency Division Multiple Access) in uplink. LTE-A (Advanced) has been improved from the LTE.
LTE-A may include new technique (e.g., a relay node and CoMP (Coordinated Multiple Point Transmit/Receive)) and can support an improved technique (e.g., MIMO extension in which the number of transmission antennas larger than the number of transmission antennas used in LTE is used).
There are factors that must be taken into consideration in this LTE-A. One of the factors is backward compatibility with terminals, a network, and so on which are designed to operate in the existing LTE. That is, it is preferred that LTE-A support terminals, a network, and so on designed to operate in the existing LTE so that they can operate in LTE-A. From this point of view, the design of a subframe structure (i.e., which radio resources will be allocated within a subframe) becomes problematic.